Here, we present new radio interferometer beamforming observations of lightning initiation using data from the Low‐Frequency Array (LOFAR). We show that the first lightning source in the flash increases exponentially in intensity by two orders of magnitude in 15 μs, while propagating 88 m away from the initiation location at a constant speed of 4.8 ± 0.1 × 106 m/s. A second source replaces the first source at the initiation location, and subsequent propagation of the lightning leader follows. We interpret the first source to be a rapidly propagating and intensifying positive streamer discharge that subsequently produces a hot leader channel near the initiation point. How lightning initiates is one of the greatest unsolved problems in the atmospheric sciences, and these results shed light on this longstanding mystery. Plain Language Summary Lightning initiation is poorly understood, in part, due to the difficulty is making detailed observations inside thunderstorms. This research elucidates the initiation process using highly sensitive imaging techniques from data acquired from the Low‐Frequency Array (LOFAR). These data indicate that lightning initiates with a cascading discharge composed of streamers before transitioning into a propagating leader. These streamers appear to propagate at a constant velocity, despite an exponential growth in number. This is an interesting result as it is not clear how it is possible to maintain both an exponential growth and a constant velocity. Key Points As seen in VHF, the first lightning signal detectable above background increases exponentially by two orders of magnitude in 15 μs Initiation is likely caused by branching streamers with constant propagation speed of 4.8 × 106 m/s during the exponential ramp‐up phase Mechanism is similar to narrow‐bipolar events, but much weaker in VHF power